Transseptal Transition Patterns During Left Bundle Branch Area Lead Implantation

Background: Continuous deep septal pacing and signal recording during implantation of left bundle branch pacing (LBBP) lead enables to monitor beat-to-beat changes of ECG and myocardial current of injury (COI) as the lead crosses the septum. Objectives: We aimed to characterize patterns of continuous QRS, ST-T and COI change - for monitoring of the lead depth and instantaneous determination of the obtained capture type: LBBP versus left ventricular septal pacing (LVSP). Methods: The ECG and COI during lead implantation were scrutinized for sudden changes of: V6 R-wave peak time; V1 initial and terminal R-wave amplitude, V3-V6 R-wave amplitude, repolarization pattern and S-wave amplitude in I, V5-V6, and COI drop. The sudden and gradual transition patterns were diagnosed depending on the presence or absence of the above beat-to-beat ECG phenomena, respectively. Results: A total of 212 pacemaker recipients were analyzed, LBBP and LVSP was obtained in 77.4% and 22.6%, respectively. There were 4.7 ±2.1 and 0.2 ±0.6 beat-to-beat phenomena in LBBP and LVSP patients, respectively. The sudden transition pattern, recognized in 80.7%, had sensitivity and specificity for LBBP diagnosis of 98.8% and 81.2%, respectively. Sudden drop of COI (29.4 ±8.5 mV to 12.8 ±4.9 mV) was observed in 53.9% patients (LBBP was simultaneously obtained in 92.7%).Conclusions: Capture of LBB during lead penetration is a beat-to-beat phenomenon. Two transseptal transition patterns were identified: sudden - typical for obtaining LBBP, and gradual - typical for obtaining LVSP. Sudden COI drop, a very observable phenomenon, also identified reaching the left subendocardial area.